There has conventionally been available a technique of obtaining an image with reduced image noise by averaging medical images respectively corresponding to two different kinds of X-ray energies. There is also available an X-ray computed tomography apparatus in which an X-ray generation unit generates X-rays having two different kinds of energy spectra. There is available a technique of reconstructing a medical image corresponding to the X-ray energy desired by the operator (to be referred to as a target energy hereinafter) by using the projection data of an object which respectively correspond to two kinds of energy spectra.
Some medical images generated by averaging, however, do not correspond to target energies. Furthermore, it requires much time to reconstruct a medical image corresponding to a target energy by using the projection data of an object which respectively correspond to two kinds of energy spectra.